Electron gun and method of assembly

ABSTRACT

An electron gun of the type comprising a series of electrodes in alignment along a gun axis. At least one of the electrodes comprises a support member with an aligned opening. An apertured member is inserted in the support member, the aperture being in alignment with the gun axis. The configuration of an inside portion of the support member is mechanically matched to the configuration of an outside portion of the apertured member, whereby the relative orientations of the members are mechanically determined on insertion of the apertured member into the support member by intimate physical contact of the inside and outside portions. Also disclosed is a method of aligning an electron gun comprising the above electrode. The support member opening is fixed in alignment with other associated electron gun components. At least a portion of the apertured member is then inserted into the support member opening, the configurations of the members being such whereby an aperture in the apertured member is mechanically aligned along the gun axis by the inserting.

United States Patent [1 1 Spalding Dec. 4, 1973 ELECTRON GUN AND METHOD OF ASSEMBLY [75] Inventor: Richard Le Roy Spalding,

Lancaster, Pa.

[73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Oct. 30, 1972 [21] Appl. No.: 302,219

Primary Examiner-Rudolph V. Rolinec Assistant ExaminerSaxfield Chatmon, Jr. Attorney-Glenn I-l. Bruestle, Sanford J. Asman and Donald S. Cohen [57 ABSTRACT An electron gun of the type comprising a series of electrodes in alignment along a gun axis. At least one of the electrodes comprises a support member with an aligned opening. An apertured member is inserted in the support member, the aperture being in alignment with the gun axis. The configuration of an inside portion of the support member is mechanically matched to the configuration of an outside portion of the apertured member, whereby the relative orientations of the members are mechanically determined on insertion of the apertured member into the support member by intimate physical contact of the inside and outside portions;

Also disclosed is a method of aligning an electron gun comprising the above electrode. The support member opening is fixed in alignment with other associated electron gun'components. At least a portion of the apertured member is'then inserted into the support member opening, the configurations of the members being such whereby an aperture in the apertured memberis mechanically aligned along the gun axis by the inserting.

5 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION The invention relates to electron guns and their alignment. It is particularly applicable to electron guns having a very fine aperture, but is not limited thereto.

Two or more apertures may be considered in perfect alignment with one another when they lie in parallel planes and have their centers located on a single, straight line perpendicular to those planes, that line being considered the axis along which they are aligned. In the manufacture of electron guns, it is a common practice to align the central apertures in a series of electron gun electrodes along a gun axis by inserting an internal beading mandrel through the apertures to hold the electrodes in alignment, and then fixing the electrodes relative to one another by applying a molten glass bead to tab members extending from the electrodes.

Some electron guns, however, include electrodes with apertures so small that it is not feasible to align the apertures mechanically by internal beading mandrel. Such apertures are generally aligned optically. Typically, a number of other associated gun components which have apertures large enough for mechanical alignment are aligned by an internal mandrel and beaded to form a partially assembled gun. Among these components is a support member having a relatively large clearance opening. A separate member having a small aperture is then placed on the support member and optically aligned thereon with the gun axis. The optical alignment is done manually by an operator who views the aperture through a microscope, centering it with respect to the clearance opening or other nearby apertures, and then fixes the small-aperture member to the support member by spot welding. Various electron gun structures, as well as techniques of assembly and alignment, are disclosed for instance in the following references:

U.S. Pat. No. 2,128,581, issued to B. C. Gardner Aug. 30, 1938, entitled Fine Beam Electron Gun, (U.S. Cl 250-27.5).

U.S. Pat. No. 3,500,520, issued to F. G. Oess Mar. 17, 1970, entitled Method of Obtaining Aperture Alignment in an Electron Gun Construction, (U.S. Cl 29-2516).

U.S. Pat. No. 3,510,926, issued to F. G. Oess May 12, 1970, entitled Electron Gun Alignment Device, (U.S. Cl 29-2519).

RCA Technical Note:

Note No.'406, January 1971, entitled Internal Beading M'andrel, by C. C. Turner et al. Optical alignment of a small aperture on a partially assembled gun is a time-comsuming, expensive step in electron gun manufacture. For some electron gun structures, intervening electrodes prevent desirable close proximity of the optical alignment microscope to the small aperture, making alignment more difficult. Furthermore, the clearance opening in the support member through which the beading mandrel passes, is much larger and less precise than the small aperture, since the mandrelmust be large enough in=diameter for sufficient rigidity. The necessarily large diameter of the clearance opening adds to the difficulty of optical alignment, since its center is not as readilydetermined optically as the center of a smaller opening.

SUMMARY OF THE INVENTION The novel electron gun has at least one electrode comprising a support member and an apertured memher, the members having configurations whereby an aperture inthe apertured member is mechanically alignedv on insertion of the apertured member into the support member by intimate physical contact of inside and outside portions of the members.

The novel gun may be assembled by a novel method comprising aligning an opening in thesupport member, fixing the support member in position with respect to the other gun components, and inserting at least a portion of the apertured member into the opening, whereby the aperture is mechanically aligned along the gun axis by the inserting.

When an electron gun comprising the novel electrode is assembled by the novel method, optical alignment of the small aperture may be performed on a member or sub-assembly separate from the partial gun assembly without the necessity of optical alignment with associated gun components after beading.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged side, sectional view of an electron gun comprising a preferred embodiment of the novel electrode assembly and aligned in accordance with the novel method of alignment,

FIG. 2 is a greatly-enlarged side, sectional view of the outer and inner aperture cup sub-assembly of the novel electrode of FIG. 1.

FIG. 3 is a greatly-enlarged top view of the outer aperture cup of the sub-assembly of FIG. 2.

I FIG. 4 is a less-enla'rged, top view of the support cup of the novel electrode of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT STRUCTURE One embodiment of the invention is a vidicon color television camera tube electron gun 10, shown in FIG. 1. The gun l0 includesa heater support 12, a cathode mount 14, a G1 electrode 16, a G2 electrode assembly 18 and a G3 electrode 20, all mechanically fixed together by two glass beads 22 sealed to strap members of the components. The electrodes are of drawn stainless steel sheet. The G1 electrode 16 has a central limiting aperture 24 about 30 mils in diameter. The G2 electrode assembly 18 consists of a support cup 26, an outer aperture cup 28, and an inner aperture cup 30. The G3 electrode 20- is a hollow cylinder about one-quarter of an inch in diameter inside.

The outer aperture cup 28 and the inner aperture cup' 30 are shown enlarged as a sub-assembly in FIG. 2. A top view of the outer aperture cup 28 alone is shown in FIG. 3. The outer cup 28 is of 5 mils thick stainless steel sheet and has an outside diameter of 0.245 inches :5 mils. Four equally spaced slots 31 about 25 mils wide extend longitudinally along the wall of the outer aperture cup 28 to permit a radial springing: action of the-wall. A cup-shaped depression, or snout 32, having closely controlled outside diameter of one-tenth inch i one-half mil and having a central outer cup aperture 34 about 30 mils in diameter, is provided in the bottom of the outer cup- 28, thereby resulting in a shoulder 36 about one-tenth inch down from the rim of the outer cup 28. The diameters of the snout 32 and the outer cup aperture 34 are concentric to within one-half mil.

The inner aperture cup 30 is of mils thick stainless The inside depth is about 50 mils. Centrally located in the bottom of the inner cup 30 is an opening38 about 30 mils in diameter. A thin electroformed nickel aperture disc 40 about 1.5 mils thick and with an inner cup aperture 42 about 2 mils in diameter is spot welded to the outside bottom of the inner aperture cup 30, the aperture 42 being centered over the larger opening 38 in the bottom of the inner cup 30. The inner aperture cup 30 is spot welded in place on the shoulder portion 36 of the outer cup 28, the inner cup aperture 42 being in alignment with the outer cup aperture 34.

FIG. 4 shows a top view of the support cup 26, which is provided with a triangular guide opening 44 in the bottom. The inside edges of the guide opening 44 are chamfered and the corners rounded. The size of the guide opening 44 is such that upon insertion therein of the snout 32 of the outer aperture cup 28, the sides of the guide opening 44 will be flexed outward slightly and will seize the snout, thereby locking it in alignment by interference fit.

METHOD For assembly of the gun, the heater support 12, cathode mount 14, G1 electrode 16, the support cup 26 alone of the G2 electrode assembly 18, and the G3 electrode 20 are mechanically aligned along a gun axis by an internal beading mandrel. This aligns the guide opening 44 in the bottom of the support cup 26 with the gun axis. The glass beads 22 are then applied molten to the strap members extending from opposite sides of the electrodes, and rigidly fix the electrodes in alignment upon cooling.

The outer and inner aperture cups 28, 30 are prealigned optically independently of the other components of the gun by rigidly holding the outer aperture cup 28 upright about the outside surface of the snout 32 while centering the'reticle of a microscope on the center of outer cup aperture 34. The microscope is then rigidly locked in position while inner aperture cup 30 is inserted into outer aperture cup 28 so that it rests on the inside surface of shoulder 36. The inner aperture cup 30 is then moved as necessary over the shoulder 36 to achieve centering of the inner cup aperture 42 with the reticle of the microscope. The inner aperture cup 30 is then spot welded to the shoulder 36 of the outer aperture cup 28 to form a pre-aligned aperture cup sub-assembly as in FIG. 2. Now the snout 32 of the prealigned aperture cup assembly is pressed into the guide opening 44 of the support cup 26 of the gun 10 so that its shoulder 36 rests firmly on the inside bottom surface of support cup 26. The outer cup aperture 34 and the inner cup aperture 42 are thereby mechanically aligned with the axis of the gun 10. The wall of the outer aperture cup 28 is spot welded to the inner wall of the support cup 26 to prevent loss of alignment by thermal stressing during operation of the gun 10.

GENERAL CONSIDERATIONS While the support member of the preferred embodiment is a round cup with a triangular opening in the bottom, numerous other configurations would be suitable for mechanical alignment of an apertured subassembly. As a practical matter, however, the support member is likely to be round with a centrally located opening, as such a configuration is readily aligned by internal beading mandrel. Also, it is advantageous to use the inside bottom surface of the support cup about the opening for determining the plane of the opening. Alternatively, the inside cup wall or other portions of the support member may be used for this if the precision of the support member is adequate to assure relative orientation of the wall and bottom.

For the preferred embodiment, that portion of the support member which by its configuration mechanically determines the alignment of the aperture member is the flat bottom portion of the support cup, including the inside edge of the opening. The opening centers the aperture of the aperture member or sub-assembly on the gun axis, and the flat bottom portion about the opening determines the perpendicular orientation of the aperture by precisely orienting the outer cup shoulder.

The apertured member may have one or more prealigned apertures. That is, the apertures are aligned relative to the geometry of the guide portion of the apertured member so that they will be aligned upon assembly of the apertured member to the support member. In the configuration of the preferred embodiment, for example, the apertures of the sub-assembly are oriented parallel to the flat shoulder surface of the outer cup and concentric with the outside diameter of the snout.

The respective portions of the configurations of the support member and the aperture member are matching if they determine completely the relative orientations of the members on assembly, so that if the configuration of the matching portion of the support member is correctly oriented with respect to the gun axis, the apertured member is necessarily aligned on insertion into the support member by virtue of the mechanical match of the members to one another. Insertion of the apertured member into the support member means insertion of any portion of the apertured member into any portion of the support member.

While the novel electrode assembly is useful primarily for electron guns having apertures too small for mechanical alignment by internal beading mandrel, it is to be understood that the novel electrode structure is not limited to such guns, but may also be used where, for instance, the relative sizes of succeeding apertures are such that an internal mandrel becomes so complex as to be impractical. For instance, where apertures go from larger to smaller to larger, a complex expanding internal mandrel would be required. For such a structure, a pre-aligned aperture electrode assembly as described would be advantageous.

Although, the gun described in the preferred embodiment has only three electrodes, the novel electrode structure may, of course, be used with a gun having any number of electrodes, and more than one of the electrodes may be of the novel type.

A special feature of the novel electrode assembly as described in the preferred embodiment is improved heat sinking for the inner cup aperture, thus permitting operation of the gun with relatively high beam currents. The foil disc in which the inner cup aperture is formed is firmly sandwiched between the shoulder of the outer aperture cup and the bottom of the inner aperture cup over the entire surface of the foil, nearly to the perimeter of the aperture itself. Thus, beam electrons which impinge on the foil do not cause excessive local heating, since the entire G2 electrode assembly makes good thermal contact to the foil and provides a relatively massive heat sink.

Another feature of the electrode of the preferred embodiment is that the apertured round metal foil disc may be electroformed to relatively high precision dimensions at relatively small cost. The outside diameter of the round foil .piece may thus be closely matched to the outside diameter of the inner aperture cup. The inner aperture cup may be placed open-end-down in a closely fitting cylinder and the apertured metal foil disc simply dropped into the cylinder on top of the inner aperture cup, thus being constrained precisely on the center of the inner aperture cup so that the aperture in the foil is concentric with the opening in the bottom of the cup. The foil is then spot-welded in place to the bottom of the inner aperture cup.

While the support cup opening of the electrode of the preferred embodiment is triangular, other configurations of openings may be used. For instance, the opening may be a round one with spring tabs extending a short distance from the edge to the center, the spring tabs bending outwardly upon insert of the snout of the outer aperture cup, thus locking it in place. Various designs for interference fit in a metal sheet opening are readily apparent. It isan important feature of the triangular opening of the preferred embodiment electrode support cup, that the force for flexing wall portions outward as the snout is pressed into the guide opening is a higher exponent function than linear functions generally associated with leaf springs. The force for flexing a uniform tongue-like leaf-spring member is approximately a constant times the tangential distance which the end tongue is displaced. For the flexing of the triangular wall portions, on the other hand, the force needed to flex the wall increases rather rapidly, the function associated with the force needed for the flexing being one having an exponent greater than one. As a result, centering of the snout is more precise with the triangular configuration for the opening than it is for leaf-spring types of configurations. The advantageous aspects of an interference fit of the snout in the opening is that the opening need not be made to high precision,-since the flexing triangular sides will compensate for variations in the size of the triangle, while still accurately centering thesnout. While a triangle appears to be particularly useful configuration for the guide opening, other polygon configurations would have similar advantages.

Since the outer cup aperture is aligned with the inner cup aperture independently of the other associated electron gun structures, the size of the outer cup aperture is relatively unimportant mechanically. No mandrel need pass through it, and optical alignment of the inner'cup aperture with it need not be performed by viewing the inner cup aperture through the outer cup apertures, but may be performed as described above in the preferred embodiment of the novel method. For some electron guns it may be desirable to make the outer cup aperture of a smaller diameter, on the same order as the inner cup aperture.

The inner aperture cup includes the apertured metal foil member across the bottom of the cup. For the preferred embodiment, the inner cup aperture is the aperture in the metal foil. The opening in the bottom of the inner aperture cup is provided for clearance about the foil aperture. it is understood, however, that the inner aperture cup may be simply one piece, with the working aperture provided centrally in the bottom, instead of in a separate metal foil member.

The novel method of electron gun assembly, made feasible by the novel electrode, has anumber' of distinct advantages. One advantage is that it permits optical alignment of the outer cup aperture and inner cup aperture as a sub-assembly, independent of the beaded and fixed associated gun structures. Alignment is thus simplified, in that handling of the main portion of the gun is reduced, closer proximity of the microscope for optical alignment to the aperture being aligned is possible, and the optical alignment is greatly speeded up by the availability of faster techniques for aligning a small sub-assembly, since it can be viewed from either end and at any distance desired. Another advantage is that the cathode, heater, and tube stem may be assembled as the associated gun structures are beaded, where with other alignment techniques they often must be assembled separately after alignment, since for alignment the apertures are viewed from the cathode end of the gun.

I claim:

1. An electron gun of the type comprising a series of electrodes in alignment along a gun axis, at least one of said electrodes comprising:

a. a support member comprising a cup having a central opening in alignment along said gun axis in the bottom thereof;

b. an apertured member inserted in said support member and having an aperture in alignment with said gun axis, said apertured member comprising: i. an outer aperture cup with a centrally apertured cup-shaped depression in the bottom, said depression being inserted fully into said support cup opening, the outside dimensions of said depression being sufficiently matched mechanically to the inside dimensions of said support member opening to prevent axial and radial play between said outer cup and support member; an inner aperture cup with an aperture in the bottom thereof fixed inside said outer cup, the outside dimensions of said inner cup being sufficiently less than the inside demensions of said outer cup to permit radial movement between said outer and said inner cups, said inner cup aperture being aligned with said outer cup aperture; and

iii. the configuration of an inside portion of said support member being mechanically matched to the configuration of an outside portion of said apertured member, whereby the relative orientations of said members are mechanically determined on insertion of said apertured member by intimate physical contact with said inside and outside portions, wherein said inside portion of said cup is the inside bottom surface and portions of the inside surface of said central opening in -the bottom.

2. The electron gun defined in claim 1 wherein said central opening is shaped generally like an equilateral triangle with rounded corners.

3. The electron gun defined in claim 1 wherein said aperture of said inner cup is in a metal foil which is fastened to the bottom of said inner cup over a larger opening in the bottom of said inner cup.

4. The electron gun defined in claim 3 wherein said support cup opening is such as to form an interference fit with the cup-shaped depression'of said outer cup.

b. an apertured member inserted in said support member, the aperture of said apertured member being in alignment with said gun axis, whereby said triangular opening of said support member mechanically holds said apertured member in position by intimate physical contact therewith.

* an a w a 

1. An electron gun of the type comprising a series of electrodes in alignment along a gun axis, at least one of said electrodes comprising: a. a support member comprising a cup having a central opening in alignment along said gun axis in the bottom thereof; b. an apertured member inserTed in said support member and having an aperture in alignment with said gun axis, said apertured member comprising: i. an outer aperture cup with a centrally apertured cup-shaped depression in the bottom, said depression being inserted fully into said support cup opening, the outside dimensions of said depression being sufficiently matched mechanically to the inside dimensions of said support member opening to prevent axial and radial play between said outer cup and support member; ii. an inner aperture cup with an aperture in the bottom thereof fixed inside said outer cup, the outside dimensions of said inner cup being sufficiently less than the inside demensions of said outer cup to permit radial movement between said outer and said inner cups, said inner cup aperture being aligned with said outer cup aperture; and iii. the configuration of an inside portion of said support member being mechanically matched to the configuration of an outside portion of said apertured member, whereby the relative orientations of said members are mechanically determined on insertion of said apertured member by intimate physical contact with said inside and outside portions, wherein said inside portion of said cup is the inside bottom surface and portions of the inside surface of said central opening in the bottom.
 2. The electron gun defined in claim 1 wherein said central opening is shaped generally like an equilateral triangle with rounded corners.
 3. The electron gun defined in claim 1 wherein said aperture of said inner cup is in a metal foil which is fastened to the bottom of said inner cup over a larger opening in the bottom of said inner cup.
 4. The electron gun defined in claim 3 wherein said support cup opening is such as to form an interference fit with the cup-shaped depression of said outer cup.
 5. An electron gun of the type comprising a series of electrodes in alignment along a gun axis, at least one of said electrodes comprising: a. a cup-shaped support member having a central opening shaped generally like an equilateral triangle with rounded corners in the bottom thereof, said opening being in alignment along said gun axis; b. an apertured member inserted in said support member, the aperture of said apertured member being in alignment with said gun axis, whereby said triangular opening of said support member mechanically holds said apertured member in position by intimate physical contact therewith. 